Molecular Mechanisms of Mitotane Action in Adrenocortical Cancer Based on In Vitro Studies

Abstract

Mitotane is the only approved drug for the treatment of advanced adrenocortical carcinoma and is increasingly used for postoperative adjuvant therapy. Mitotane action involves the deregulation of cytochromes P450 enzymes, depolarization of mitochondrial membranes, and accumulation of free cholesterol, leading to cell death. Although it is known that mitotane destroys the adrenal cortex and impairs steroidogenesis, its exact mechanism of action is still unclear. The most used cell models are H295-derived cell strains and SW13 cell lines. The diverging results obtained in presumably identical cell lines highlight the need for a stable in vitro model and/or a standard methodology to perform experiments on H295 strains. The presence of several enzymatic targets responsive to mitotane in mitochondria and mitochondria-associated membranes causes progressive alteration in mitochondrial structure when cells were exposed to mitotane. Confounding factors of culture affecting in vitro experiments could reduce the significance of any molecular mechanism identified in vitro. To ensure experimental reproducibility, particular care should be taken in the choice of culture conditions: aspects such as cell strains, culture serum, lipoproteins concentration, and culture passages should be carefully considered and explicated in the presentation of results. We aimed to review in vitro studies on mitotane effects, highlighting how different experimental conditions might contribute to the controversial findings. If the concerns pointed out in this review will be overcome, the new insights into mitotane mechanism of action observed in-vitro could allow the identification of novel pharmacological molecular pathways to be used to implement personalized therapy.

Keywords: H295 strains; adrenocortical carcinoma; mitotane.

Figure 1

Mitotane impairs the function of the adrenal cortex. In the left part of the figure, the different zones of the adrenal cortex are schematized; the main enzymes involved in the biosynthesis of steroid hormones are also indicated. As depicted in the right part of figure, mitotane action, identified by in vitro experiments, involves several mechanisms ranging from the deregulation of mitochondrial key genes at a transcriptional and functional level, to the MAMs dissociation, the rupture of mitochondrial membranes, and altered cholesterol transports/metabolism. Mitotane action for each enzyme is indicated by a red mark. Figures have been created modifying an image set from Servier Medical Art (SMART) http://smart.servier.com/ (19 July 2021).

Figure 2

Physiological regulation of cholesterol uptake, synthesis, and steroidogenesis and proposed mitotane effect/mechanism of action. In the left part of the figure is indicated the physiological mechanism that regulates the absorption/synthesis of cholesterol and steroidogenesis. As depicted in the right part of the figure, mitotane induces in vitro the dissociation of MAMs and the blockade of cholesterol transport/synthesis and steroidogenesis. Accumulation of free cholesterol in cells causes ER stress, apoptosis, and cell death. The action of mitotane for each enzyme is indicated by a red mark. Figures were created modifying an image set from SMART http://smart.servier.com/ (19 July 2021).